Although more harsh and stern than his counterpart in the prime universe, relatively speaking, Forrest seemed to honestly care about the overall well-being of his ship and crew, and was legitimately concerned when a Terran Empire task force was destroyed fighting rebels at Tau Ceti.

In 2155, Commander Archer mutinied against Forrest, and threw him into the brig. Forrest later expressed surprise at this action, claiming that he chose Archer as his first officer because he thought the commander had no ambition.

Forrest, who had allies of his own on board Enterprise, retook command of the ship and put Archer in the agony booth for over ten hours. Forrest later discovered that Archer had taken the ship into Tholian space and could not unlock the controls. Fleet AdmiralGardner learned of Archer's mutiny and his ambitious plans, and felt that Archer's mission may have had some validity. Forced to allow Archer to give an officer's briefing, he heard Archer's intelligence that the Tholians had obtained a Starfleetvessel from a parallel universe and a century in the future – the USS Defiant. Archer made an impassioned argument that the technology of this future ship could be used by the Empire to help crush the rebellion. Unable to override the controls, and swayed somewhat by Archer's arguments, Forrest reluctantly carried out the mission. However, he made it clear to Archer that his act of betrayal would not be forgiven or forgotten.

Enterprise is destroyed

When sending an away team led by Archer to the ship, Forrest ordered Commander T'Pol to do what she could to make sure that Archer did not come back alive. During the mission, however, Enterprise was attacked by the Tholians. Shortly thereafter, Forrest was killed in a Tholian attack, choosing to remain aboard Enterprise to buy time for the rest of the crew to evacuate the ship in the escape pods. (ENT: "In a Mirror, Darkly")

Like his counterpart, Maximilian Forrest was portrayed by Star Trek veteran Vaughn Armstrong, and is to date, his most recent on-screen appearance.

The mirror universe Forrest's name comes from the episode's script; in the episode, he is only referred to as "Captain Forrest". Also in the script, Forrest was described as sleeping in his cell just before he is released from the brig and then being awoken by the jailbreak. In the episode, however, he is fully awake throughout that scene. Regarding his self-sacrifice, the script likened him to his doppelgänger from the prime universe, commenting, "For a moment, Forrest appears as heroic and as selfless as his counterpart in our universe."